>2 wrote:
>>>>** RCA's Rocky Point Investigation was somewhat specious since there is
>>>>no such thing as disappearing gas and vanishing "barnacles".
>>>
>>>Well, so much for RCA then! And so much for the G-E Research Labs,
>>
>>G. W. Flyer of GE (1935), H. F Dittrich of Phillips (1958), and ARRL's F.
>>E. Handy (1926) arrived at a different conclusion than RCA's Rocky Point
>>investigation. [Dittrich, H. F.; *Tubes for R. F. Heating*; N.V.
>>Phillips Gloeilaampenfabrieeken--Eindhoven, the Netherlands. Section
>>5.8, ''Parasitic Suppression Circuits'' begins on page 96.]
>>
>
>THE WHOLE POINT is that there's more than one possible explanation!
>
** agreed
>Sometimes it's parasitic oscillations, sometimes it's vacuum arcs,
>sometimes it's arcs outside the tube, and so on... it very hard to tell
>from the evidence left behind.
>
>Anyone who believes in only one explanation will be wrong at least some
>of the time - that much we do know for sure!
>
** I have seen gassy tubes, but I have never seen one damage a VHF
parasitic suppressor resistor..
>>>and all the R&D work that went into their book on 'Vacuum Arcs'; and
>>>Gossling's work with the UK General Electric Company (no relation) and
>>>the BBC; and all the other workers who have found ample evidence for
>>>arcs... including Eimac.
>>>
>>Eimac reference, please.
>>
>The same Eimac reference I have given you at least three times before!
>Bulletin 17 on 'Fault Protection', a copy of which is at
>www.ifwtech.co.uk/g3sek/misc/bull17.pdf
>
>Eimac says: "An arc is a self-sustained discharge of electricity,
>between electrodes in a vacuum environment... The arc supports large
>currents by providing its own mechanism of electron emission... Since
>any high voltage vacuum device may arc at one time or another, some
>means of protection is advised in all cases."
>
** Protecting an already gassy tube makes little sense to me.
>So Eimac clearly understand that vacuum arcs are one possible
>explanation of current surges.
>
>>The problem with Rocky Point Effect is that there is apparently rarely
>>evidence to support it during kaput tube/valve autopsies. I have yet to
>>autopsy a tube with an anode arc-mark and that includes tubes that are
>>gassy due to a leaky seal.
>
>You may have led a sheltered life. There are some excellent autopsy
>photos of arced Russian tubes (again, referenced here before) at
>www.ifwtech.co.uk/g3sek/misc/gs35a.jpg
>www.ifwtech.co.uk/g3sek/misc/gs35g.jpg
>
** I have seen them.
>These are corresponding marks on the anode and mesh grid of the same
>tube. Note the multiple arc marks (very much provoked by running the
>tube above 4.5kV and at well over 2kW out on 144MHz).
>
>Each time that the tube arced, it recovered its vacuum and ran OK for a
>while. Note that carefully: tubes do recover their vacuum after an arc.
>This cycle was repeated five times (count the marks) until the last big
>zap, when owner decided to scrap the tube and open it up.
** To prove that an anomaly was due to loss of vacuum or a "barnacle",
the tube would have to be high-pot. tested immediately after the event.
>
>Obviously these are very severe arcs, but much less noticeable arcs
>would be enough to do a lot of damage in an unprotected PA.
>
>> Another problem is that it seems unlikely
>>that (since sound travels in air) an amplifier could produce a stentorian
>>bang from an arc inside the vacuum. I have not yet found an amplifier
>>that produced a loud bang that did not have a damaged VHF parasitic
>>suppressor resistor. This tells me that there is a quite likely a VHF
>>connection with loud bangs.
>
>Vacuum arcs and runaway parasitic oscillations are both possible - and
>both result in a very large current surge. I believe it's the current
>surge in the external components that causes the audible bang, if there
>is one.
** Owners of amplifiers that had a stentorian bang reported seeing an
arc in the vicinity of the anode circuitry.
>There are enough reports of blown meter shunts, zeners etc to
>explain a lot of bangs from unprotected amps.
** In my opinion, none of these would be likely to generate that much
noise.
>
>To repeat my main point: NOBODY can tell what happened on any particular
>occasion, without a detailed post-mortem of the whole amp... and maybe
>not even then.
>
** The first thing I measure is tube leakage. The second is the
resistance of the suppressor resistor.
>
>--
cheers, Ian
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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